A vast amount of the front line research in nuclear structure physics is performed with radioactive ion beams nowadays. The next generation facilities are being built in the world-leading countries. The RIBF in RIKEN, Japan started its operation recently, while the first phase of the SPIRAL2 facility in GANIL, France is expected to be ready in 2012. These top-notch devices open up frontiers for experimental investigations and make it possible to discover new effects, which might change our view on nuclei.

The main aim of the proposal is to show that the proton-neutron correlation measured by the neutron effective charge has a strong binding energy dependence, that is, while a weakly bound neutron behaves more or less like a free entity, a deeply bound neutron, even if it is a single nucleon above a closed shell, looses its individuality. For this purpose, on one hand we plan to uncover different phenomena of the weakening of the proton-neutron correlation in loosely bound neutron rich nuclei via searching for pure neutron excitations and for decoupled proton-neutron excitations. On the other hand, we intend to determine whether there is a strengthening of the proton-neutron correlation close to the proton drip line by looking for increased neutron effective charges. As a byproduct, other aspects of the proton-neutron correlation, leading to the change of the shell structure, such as cluster-like or other special correlations can also be studied.

The present proposal is an updated version of the proposal No. 84118, which was close to be financed last year. The salery of the post doc has been taken out and the rest of the budget was tightened as much as possible.

Investigations of the proton-neutron correlation has been performed at the leading nuclear physics laboratories all over the world within the frame of international collaborations. The xperiments have been performed by use of in-beam gamma ray spectroscopy or beta decay methods mainly at RIKEN, but also in GANIL, Legnaro, ILL or NSCL.
Different aspects of the proton-neutron correlations have been studied in the present project in the framework of several collaborations. The most important results obtained are as follows: Observation of weakening of the effective proton-neutron interaction close to the neutron drip line in 26F, of a bubble like proton distribution in 34Si, or of the absence of proton-neutron T = 0 condensate at A = 62, shell model extrapolation was made for the stability of the N=82 shell closure, indirect evidences has been given on the double magic character of 78Ni, multiple chiral doublet bands of identical configuration were found in 103Rh, and anomalous large transition probability in 104Sn, as well as deformed shell closure at N=100 in light rare earth nuclei.
A large amount of experimental information has been collected on the structure of nuclei next to the N= 40, 50, 82 and 132 shell closures which helps to understand the new phenomena observed approaching the neutron drip line.